If you upgrade your speed you can't repair the tank. I can add max HP with armor upgrades, but you can't repair a vehicle while inside it, and now my tank is going so fast that bots can't repair it either.

I've set it off in a very wide circle with the help of some landfill. Had to destroy trees with a console command though, since hitting the trees offsets your circling.

Speed just goes up way too fast. I figured with the rate of increase for the other stats I'd try putting in 3-5 locomotives and see how that worked, but now it's just way too fast. I can't maneuver or tell what's going on around me

A single train engine bumps your speed up from 32 kph to 216 kph. Also, the speed bonus does not apply while on water. You also can't turn while on water, except for the automated course adjustment slider thing

Repair by inserting repair packs into the upgrade chest.

Also locomotives weren't supposed to upgrade speed that quickly!